The experiments outlined in this proposal are designed to accomplish two objectives. The first is to examine some aspects of the kinetics of the Na-K pump. Specifically, we intend to determine the effect of the concentration of one of the transported species (Na or K) on the affinity of the pump for the other species (K or Na). By accomplishing this it seems likely that we will have some basis for determining whether a model in which Na and K are moved simultaneously in opposite directions or one in which the ions are moved sequentially best describes the operation of the pump. The second objective is to perform studies designed to throw some light on the mechanism by which an IgG antibody alters the affinity for intracellular K of the Na-K pump in low potassium (LK) goat cells. It seems possible that the antibody can accomplish this by either combining directly with the pump or by combining with some other site on the cell membrane and secondarily changing the environment of the pump. The latter possibility would suggest that the pump is capable of cooperative behavior. The problem will be approached by counting the number of antibody binding sites and comparing it to the number of pump sites, by determining whether the antibody is associated with the pump in disrupted membranes, and by determining whether the antibody effects other membrane properties in addition to Na-K transport.